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312 Refining Biomass Residues for Sustainable Energy and Bioproducts

0.5 mm where the cellulose conversion ratio increased from 61% to 79%. Thus
these studied showed that the particle size may or may not have a significant impact
on the delignification efficiency and reducing sugar content, and the choice of the
reactor used and type of biomass used in the studies may affect the result.

14.2.2.3 Effect of moisture
Among other parameters, moisture also plays an important role in the ozonolysis
process. Many researchers studied the effect of moisture content to optimize the
process condition and improve delignification and sugar release yield. The moisture
content acts as a mass transport medium that regulates the radical production rate,
therefore affecting the efficacy of the ozone treatment.
Travaini et al. (2016c) stated that the moisture content interacts closely with
types of reactors used. The mixed reactors provide homogeneous ozone concentra-
tion that is related to high water content, while the plug flow reactors, with its con-
centration gradient along its length, promote lower moisture content. The
ozonolysis reaction starts with ozone conversion from gas phase to free water and
later converts to bounded water before finally establish ozone reactions with the lig-
nocellulosic biomass (Li et al., 2015b). The optimum moisture content is different
depending on the biomass type. Neely (1984) stated that the optimum moisture con-
tent is strongly linked to the fiber saturation point. At lower concentration the bio-
mass is not completely reacted with ozone resulting a shorter breakthrough. The
biomass pores are exposed when the water concentration is excessive, which will
break the thick film of water, resulting in a large ozone residence time and the
decomposition of hydroxyl radicals (Travaini et al., 2016c).
Miura et al (2012) studied the relationship between ozone consumption and
chemical composition with moisture content of wood. The report showed that the
moisture content of 68% and 38% resulted in a significant change in the ozone con-
sumption of 65% and 96% (Miura et al., 2012). At a higher moisture content of
40% the ozone consumption decreased due to the absence of free water around the
material. On the other hand, the interactions between particle sizes and moisture
content were studied by Li et al (2015) who found that the optimal moisture content
can be regulated by finding the water activity.
The ozonolysis of sugarcane bagasse in fixed-bed reactor has been studied by
Travaini et al. (2013) and obtained 46% glucose yield at 80% (w/w) moisture con-
tent (Travaini et al., 2015). Meanwhile Souza-Corrˆ ea et al. (2013) found that the
optimum moisture content at 50% for ozonolysis of sugarcane bagasse for the effect
of moisture content of 10%, 25%, 50%, and 75%. The agricultural residues have
higher optimal water contents due to their higher ability to bond water compared to
woody biomass. Meanwhile, the wheat straw in the fixed-bed reactor for moisture
content between 30% and 90% (w/w) has been investigated by Bule et al. (2013)
who found the optimal glucose release at 90% moisture content. The influence of
moisture content between 20% and 40% on spent shiitake culture was studied by
Ueda et al (2015) and found the lignin was not effectively degraded when the water
content used is higher than 60%.